JEDDAH, SAUDI ARABIA
— Apparently concerned that fighting in Iraq could spill over into this oil-rich kingdom, Saudi Arabia is considering a major fortification of its 500-mile border with Iraq.

"The government is thinking of building an electrified fence along the whole border with Iraq in case things go really badly in Iraq, and it starts falling apart," says a security adviser to the Saudi government, who spoke on condition of anonymity because the government has not made any official announcement of such plans.It has, however, admitted that it is looking at strengthening its border defenses.

"We are currently conducting a study on technical defense systems which we can use to beef up security measures along the border," Mansour al-Turki, an Interior Ministry spokesman, told the daily Al-Riyadh.

The border with Iraq lies mostly in barren desert. A 20-foot-tall sand berm that runs its entire length provides the first line of defense. Parallel to that is a second berm and a tall fence topped with barbed wire, with a six-mile-wide no-man's land separating the two barriers.

But despite the barriers and extensive electronic surveillance by Saudi border guards using motion detectors and night-vision cameras, some US critics have claimed that suicide bombers have been sneaking across the Saudi border into Iraq to join the insurgency.

One high-level European diplomat in the Saudi capital, Riyadh, defended the Saudi effort at securing its border in Iraq. "I don't think border security is really a problem," says the diplomat, who requested anonymity because of the issue's sensitive nature. "We're impressed with what the Saudis are doing. The problem is with the Americans in Iraq. The American-controlled side of the Iraqi border is less secure because they don't have enough troops deployed there."

According to a recent report compiled by Saudi defense analyst Nawaf Obaid, using government data, the kingdom has already spent $1.8 billion securing its border with Iraq since 2004. "But this amount has been mostly for the deployment of additional troops on the border and not for actual physical defenses," says Mr. Obaid in a telephone interview.

In his report, "Meeting the Challenge of a Fragmented Iraq: A Saudi Perspective," which was published this month by Georgetown University's Center for Strategic and International Studies, Obaid calls for the creation of a permanent border security committee to tackle cross-border issues between the kingdom and Iraq.

"One of the most critical tasks facing such a committee [is to strengthen] security on the Iraqi side of the border. It is in the interests of both Saudi Arabia and Iraq to confront challenges such as smuggling and terrorist infiltration that an insecure border presents," writes Obaid.

One of the kingdom's major concerns is that Iraq's sectarian violence may spill over and agitate tensions between Saudi Arabia's Sunni Muslims, a majority of the population, and its minority Shiite community. Adherents of two sects that split centuries ago, Sunnis and Shiites have a rocky history of coexistence in many countries.

In Saudi Arabia, King Abdullah has tried to ease tensions between the country's Sunnis and its Shiites, who are concentrated in its oil-rich eastern province. But Shiites are still often discriminated against in education and the job market and are regularly criticized by Salafist preachers - hard-line Sunnis - who claim that Shiites are not real Muslims.

"The Saudis are afraid of what may come out of Iraq in the future, because of the threat of Al Qaeda infiltrators and Shia [Shiite] fighters coming across the border," says Faris Bin Hizam, a Saudi journalist and specialist on Al Qaeda, in a phone interview from Dubai, U.A.E.

"The new wave of Shias coming out of Iran and Iraq are more dangerous than the Shias in 1979 during the Iranian Revolution that brought Khomeini to power. Then, there was Saddam Hussein to oppose them. Now, he isn't in power anymore," explains Mr. Bin Hizam. "I see a very difficult future for the whole region as it's not only Saudi Arabia that fears a Shia uprising, but other Gulf countries, Jordan, and Egypt as well."

But it is not only on the Iraqi border that Saudi Arabia feels threatened. Its 900-mileborder with Yemen has long been a transit point for smugglers of weapons and drugs, and terrorists sneaking into the country. Running through mountains in the west into Saudi Arabia's barren Empty Quarter in the east, the border with Yemen has been difficult to patrol and impossible to seal off completely. Smugglers have even reportedly trained goods-laden mules to avoid Saudi border guards.

In an attempt to control the border, Saudi Arabia began building a fence but was forced to freeze the project in 2004 after strong protests from the Yemeni government.

"The Saudi government has a habit of overspending on security, and the Yemeni fence project will cost upwards of over $10 billion once it is finished," says Ali al-Ahmad, director of the Institute for Gulf Affairs, a Saudi opposition think tank in Washington. In an e-mail exchange, Mr. Ahmad contends that the security fence along the Yemeni border has failed to stop weapons, drugs, terrorists, and illegal workers from "flooding" into the kingdom.

Ahmad believes that the Yemeni border poses a greater risk than the Iraqi border, in part because Yemen is a key weapons source for Al Qaeda operatives in Saudi Arabia. The sparsely populated border with Iraq is also easier to protect, he says, lending itself to electronic and visual surveillance methods, which are cheaper than a new fence.

Bin Hizam agrees with Ahmad, saying the length of the Iraqi border makes building an electrified fence along the entire length of it economically unviable. But Western security and construction firms are reportedly standing ready.

"A consortium of British, French, and American firms are interested in bidding for a contract to improve border security," the European diplomat confirmed.